The present invention relates to a water-soluble film comprising an anionic group-modified polyvinyl alcohol (polyvinyl alcohol being hereinafter referred to as PVA resin) as a main component. More particularly, the invention relates to a water-soluble film which can maintain its original water solubility without causing gelation when applied to the use in packaging of various chemicals such as detergents, particularly detergents containing a boric substance, especially sodium perborate, and the solubility of which is not affected even if the film is thrown in an aqueous solution containing a boric substance, especially sodium perborate.
PVA resin films have been used, utilizing the water solubility, for unit-dose packaging (unit pack) of chemicals such as agricultural chemicals and detergents, wherein a unit dose of a chemical is packed in a bag made from a PVA resin film.
As a film used for preparing water-soluble unit packaging bags are known, for instance, a water-soluble film comprising a modified PVA resin containing 1 to 10% by mole of carboxyl group and having a degree of hydrolysis of at least 80% by mole and a viscosity of at least 46 cPs measured at 20° C. with respect to 4% by weight aqueous solution thereof (e.g., JP-A-4-170405), a water-soluble film comprising a modified PVA resin having an anionic group modification ratio of 2.0 to 40.0% by mole and a water-insoluble or slightly water-soluble fine powder having an average particle size of at most 150 μm (e.g., JP-A-10-060207), and a water-soluble film comprising a PVA resin incorporated with, per 100 parts by weight of PVA resin, 5 to 30 parts by weight of a plasticizer, 1 to 10 parts by weight of starch and 0.01 to 2 parts by weight of a surfactant (e.g., JP-A-2001-329130).
Such known water-soluble films can be utilized for packaging various chemicals. Chemicals to be unit-packaged are frequently incorporated with boric acid substances, particularly sodium perborate, for the purpose of impartment of bactericidal or insecticidal action, prevention of putrefaction, and oxidation bleaching. Known PVA resin films as mentioned above react with the boric acid substances and become insoluble in cold water to result in loss of the function, if chemicals containing boric acid substances even in a small amount are packaged in the films, or if the films are thrown in an aqueous solution containing the boric acid substances even if the chemicals packaged in the films do not contain the boric acid substances.
In order to eliminate such defect, as a material for packaging chemicals containing boric acid substances is proposed a water-soluble film made from a composition comprising 100 parts by weight of a PVA resin and 2 to 100 parts by weight of a compound obtained by addition reaction of 1 to 4 moles of an alkylene oxide to 1 mole of a tetra- to hexahydric alcohol (e.g., JP-A-9-272772). Since the addition reaction product of alkylene oxide to polyhydric alcohol is incorporated as a boric acid catcher into PVA resin, the proposed PVA resin film has the advantage that the gelation of PVA resin caused by the reaction of PVA resin and boric acid can be prevented when the PVA resin is in the form of a film, in other words, deterioration in the water-solubility of the PVA resin film during the storage of packages can be prevented. However, in the state that a package is put in water and once the system turns to an aqueous solution of a boric acid substance by dissolution of a part of the PVA resin film, or in the state that the package is directly put in an aqueous solution of a boric acid substance, it is difficult to completely dissolve the PVA resin film in the system. Therefore, the proposed PVA resin film has the disadvantage that the gelled PVA resin remains and, if the film is used for packaging a detergent, it sticks to clothes, so the proposed film is not satisfactory in practicability.
Accordingly, an object of the present invention is to provide a water-soluble film which is suitable for packaging chemicals containing a boric acid substance, particularly sodium perborate, and which exhibits an excellent water-solubility without being gelled even in an aqueous solution of a boric acid substance, particularly sodium perborate, to say nothing of during the storage of packages wherein chemicals containing a boric acid substance are packaged in the film.
This and other objects of the present invention will become apparent from the description hereinafter.